ABSTRACT
In general terms, specific language impairment (SLI) is easy to define: It is diagnosed when a child fails to make normal progress in language learning for no obvious reason. In practice, however, this simple characterization is deceptive. Deciding who should or should not be regarded as having SLI can be fiendishly difficult. In this chapter, I discuss three issues that arise when defining diagnostic criteria for SLI: (a) the question of whether there should be a substantial discrepancy between IQ and language level, (b) comorbidity with and differentiation from other developmental disorders, and (c) heterogeneity of developmental language impairment. Experts differ in their recommendations as to how these issues should be addressed. My own view is that much of the controversy arises because people are looking for a single diagnostic solution to a range of different problems.
